1. Technical Field
This invention relates generally to in-vitro diagnostics, and more particularly to apparatus and methods for conducting thermally controlled in-vitro diagnostics.
2. Related Art
Biological diagnostic tests are a fundamental component in the process of determining the state or condition of a biological environment. These environments include, but are not limited to, human healthcare, agriculture, live stock management, municipal systems management, and national defense. Molecular tests that utilize nucleic acid detection provide an incredibly competitive level of specificity, sensitivity, and rapid timing from sampling to result. Nearly all nucleic acid detection approaches require signal amplification, such as Polymerase Chain Reaction (PCR), to generate detectable amounts of the targeted nucleic acid segment. Traditional mechanisms used in nucleic acid detection tests requiring PCR utilize high powered, immobile, non-disposable equipment to achieve large temperature gradients with high resolution. Although, these mechanism prove useful to obtain the test results desired, they are costly and are limited to use in fixed locations, given they require large, immobile equipment.
An assay is a sequence of steps or procedures used measure the presence or absence of a substance in a sample, the amount of a substance in a sample, or the characteristics of a sample. An example of a common point of care assay, or an assay conducted by a layperson is a blood glucose test. In this test, the blood is mixed with glucose oxidase, which reacts with the glucose in the sample, creating gluconic acid, gluconic acid in turn, reacts with a chemical in the assay called ferricyanide, producing ferrocyanide. Current is passed through the ferrocyanide and the impedance reflects the amount of glucose present.
Thermal cycling is a common method of accelerating a chemical reaction or promoting a biological event. Thermal cycling is a used to amplify segments of nucleic acid by via PCR. As shown in FIG. 1, in an example of a thermal cycling process, high temperature thermal cycling is used to physically separate two stands of a double helix DNA. This process is commonly referred to as denaturing, wherein the linked strands of the DNA are separated into two single strands. Temperatures maintained during denaturing are typically in the range of 94° to 96° C. The two separated strands from the denatured DNA are used as templates to logarithmically replicate identical copies of the targeted segment of DNA. Upon reducing the temperature to approximately 52° C., synthetically designed primers bind to, or “anneal” to the template DNA strands such that they flank both sides of a target segment of denatured strands of DNA. DNA Polymerase and other cofactors then cause the primer to extend fully along the denatured strands of DNA and thus, a new double stranded piece of DNA is generated, wherein a lower controlled temperature in the range of 70° to 80° C. is maintained.
The thermal cycling discussed above during denaturing and DNA replication is typically controlled in a laboratory machine. The machine includes electrical heating and cooling elements configured in electrical communication with thermal sensors in a closed loop control scheme. These machines are relatively large, immobile and expensive.